Post-consumer polyethylene terephthalate (PET) which is primarily provided by or derived from plastic soft drink bottles, can be readily obtained from material recovery facilities. Such material, however, exhibits relatively low and heterogeneous, or a wide distribution of, intrinsic viscosity (IV) values, and in the past, this characteristic has prevented such PET materials from being directly used to produce products, such as, for example, high-performance plastic strapping, which in fact require relatively high and homogeneous intrinsic viscosity (IV) values. It was one of the discoveries of the invention disclosed within the aforenoted related U.S. patent application Ser. No. 08/794,538 that such heterogeneity, or relatively wide distribution, of the intrinsic viscosity (IV) values of the PET material did not in fact adversely affect the production of such high-performance strapping, and the present invention further defines the intrinsic viscosity (IV) parameters or values of the PET starting materials used in connection with the processing of such PET materials into high-performance plastic strapping.
In accordance with prior art processing techniques, the PET material, whether post-consumer and/or non-post consumer material, was initially chopped into flakes and chunks, and the flakes and chunks were extruded into pellets. The chopped PET materials had a relatively low and wide range of IV values because the various soft drink bottles, for example, were manufactured by different companies using different materials exhibiting different IV values. The IV values were typically within the range of 0.60-0.80 dl/g. In accordance with such prior art processing techniques, it was further believed that in order to make a high-performance product, such as, for example, high-performance plastic strapping, from such post-consumer PET materials, it was necessary that the materials exhibit or achieve a relatively high and narrow range of IV values after the solid state processing which therefore required, as an initial step, the pelletizing of the flakes before commencement of the solid state polymerization. When the PET pellets are then subjected to solid state polymerization (SSP), the pellets would have their IV values raised and exhibit a relatively high and narrow range of IV values whereby such enhanced pellets could then be used to produce high-performance products, such as, for example, high-performance strapping.
As noted hereinabove, in accordance with the noted prior art processing techniques, the prior art solid state polymerization (SSP) of the PET materials commenced with pellets of uniform geometry. Such prior art solid state polymerization (SSP) of the pellets, however, required an inordinate amount of time, that is, approximately twelve to nineteen hours, to complete in order to produce the desired strapping, and it was not appreciated, until the invention disclosed within the aforenoted U.S. patent application Ser. No. 08/794,538, that a heterogeneous mixture of flakes and chunk-like PET materials could undergo direct solid state polymerization, without necessarily being initially pelletized, to the same or higher average IV values as those of the prior art pellets, and in a significantly faster manner, that is, upon the order of one-quarter the time required for the solid state polymerization of the pellet materials.
More specifically, it was believed that, in accordance with the teachings of the prior art, flakes with a wide distribution of IV values could not be solid stated directly and must firstly be pelletized to a state which is "suitable" for the production of high performance strapping. In this environment, the term "suitable" meant that the materials not only exhibited a relatively high average IV value, but in addition, the materials also exhibited a relatively narrow range of IV values. The solid state polymerization of the pellets was intended to result in, and did in fact result in, materials exhibiting a narrow IV value range which those skilled in the art believed was necessary in order to make a high-performance product. However, the resulting prior art strapping exhibited average IV values which were not greater than 0.90 dl/g. In contrast, and contrary to the aforenoted teachings of the prior art, it was discovered that high-performance plastic strapping fabricated in accordance with the processing techniques disclosed within the aforenoted U.S. patent application Ser. No. 08/794,538 exhibited average IV values which were greater than 0.90 dl/g. Therefore, in accordance with the teachings of the invention embodied within the aforenoted U.S. patent application Ser. No. 08/794,538, high-performance plastic strapping could be commercially manufactured in an economical manner using PET materials, having a relatively wide distribution of IV values, and as a result of undergoing solid state polymerization directly from flaked materials which do not have to be initially pelletized.
The prior art is also exemplified by the type of solid phase polymerization processing as that disclosed within Knox, U.S. Pat. No. 3,767,601, wherein the solid phase polymerization of waste PET is disclosed without initially pelletizing the same. However, again, as was true or characteristic of the aforenoted type of prior art, the waste PET film used as the starting materials in connection with the process disclosed within the Knox patent is gathered from a commercial production run of manufacturing PET film and is characterized by a relatively low and very narrow range of intrinsic viscosity (IV) values, such as, for example, 0.50-0.55 dl/g. In accordance with the teachings of the present invention, however, and contrary to the disclosure or teachings of Knox, the initial starting materials have a much wider distribution or diversity of IV values, such as, for example, within the range of 0.60-0.80 dl/g, and as high as 0.90 dl/g, and more particularly, the difference in the intrinsic viscosity (IV) values between different ones or types of starting materials is at least, or greater than, 0.05 dl/g, is probably at least 0.10 dl/g, and the differential range of intrinsic viscosity (IV) values of the starting materials can be 0.10-0.30 dl/g.